The present invention relates to a semiconductor device for a light valve and a production method thereof. More specifically, the present invention relates to a transparent semiconductor device and a production method of the same which is utilized as a driving substrate of a flat light valve such as an active matrix liquid crystal display device.
FIG. 26 shows a general construction of the driving substrate used in the active matrix liquid crystal display device. The driving substrate 1001 is formed integrally thereon with a pixel array 1002 and a peripheral drive circuit including an X-drive 1003 and a Y-drive 1004 by an IC fabrication process.
FIG. 27 schematically shows the pixel array. A thin film transistor (TFT) 1007 is formed for switching a pixel at each intersection between plural scan lines 1005 and plural signal lines 1006. The TFT 1007 is connected at its gate electrode to corresponding scan line 1005, connected at its source electrode to a corresponding signal line, and connected at its drain electrode to a corresponding liquid crystal pixel 1008. The liquid crystal pixel 1008 is composed of a liquid crystal layer sandwiched between the driving substrate and a counter substrate. While the scan lines 1005 are scanned to select and open the TFTs 1007, the signal lines 1006 are accessed to write an image signal into the corresponding liquid crystal pixels 1008.
The TFT is composed of a semiconductor thin film material conventionally selected from polysilicon or amorphous silicon. However, these materials have a relatively low mobility, hence it would be difficult to utilize the TFT for a transistor element of the peripheral drive circuit. In view of this, recently another technology has been developed such that a single crystal silicon (monosilicon) transistor is formed to constitute a peripheral drive circuit element, as disclosed for example in Tokkaihei 3-100516. This prior art utilizes a composite substrate comprised of a monosilicon wafer laminated on another wafer composed of a transparent insulating material such as quartz glass. The monosilicon wafer is partly removed by etching so that a pixel array is formed on an exposed surface of the quartz glass wafer, while a pixel array is formed on an exposed surface of the quartz glass wafer, while a peripheral drive circuit is formed in the remaining part of the monosilicon wafer.
However, when a high temperature IC process over 1000.degree. C. is applied to the composite substrate comprised of a laminate of the quartz glass wafer and the monosilicon wafer, the substrate is deformed due to thermal expansion difference to thereby disadvantageously hinder a yield rate and reliability. In view of such a problem of the prior art, an object of the invention is to construct a semiconductor device for a light valve by using a stable substrate free of thermal deformation.